https://www.selleckchem.com/products/d34-919.html 3±41.7µmol/L) and returned to normal after 180min (8.4±0.6µmol/L). Twenty-four hours urinary fructose levels were significantly lower in low fructose consumers when compared to normal and high fructose consumers (median 36.1µmol/24h, IQR 26.4-64.2; 142.3µmol/24h, 98.8-203.0; and 238.9µmol/24h, 127.1-366.1; p=0.004 and p<0.001, respectively). Fructose concentrations can be measured accurately and precisely with this newly-developed UPLC-MS/MS method. Its robustness makes it suitable for assessing the value of fructose in clinical studies. Fructose concentrations can be measured accurately and precisely with this newly-developed UPLC-MS/MS method. Its robustness makes it suitable for assessing the value of fructose in clinical studies.Coffea liberica possesses stimulant properties without accumulating the methylxanthine caffeine. The basis for this peculiar observation is that methylurates (e.g., theacrine and methylliberine) have replaced caffeine. The stimulant properties of methylurates, alone and in combination with caffeine, have recently been investigated. However, human pharmacokinetics and LC-MS/MS methods for simultaneous measurement of methylxanthines and methylurates are lacking. To address this deficiency, we conducted a pharmacokinetic study in which subjects (n = 12) were orally administered caffeine (150 mg), methylliberine (Dynamine™, 100 mg), and theacrine (TeaCrine®, 50 mg) followed by blood sampling over 24 h. Liquid-liquid extraction of plasma samples containing purine alkaloids and internal standard (13C-Caffeine) were analyzed using a C18 reversed-phase column and gradient elution (acetonitrile and water, both containing 0.1% formic acid). A Waters Xevo TQ-S tandem mass spectrometer (positive mode) was used to detect caffeine, methylliberine, theacrine, and IS transitions of m/z 195.11 → 138.01, 225.12 → 168.02, 225.12 → 167.95, and 198.1 → 140.07, respectively. The method was validated for precis